Ge_nMn(n=1-13)团簇的稳定结构、电子性质和磁性研究

The geometrical structure,electronic structure and magnetism of Ge_nMn clusters

基于全电子的密度泛函理论,对GenMn(n=1-13)团簇的结构和电子、磁特性进行了研究,结果表明:GenMn(n=1-7)团簇的最稳定结构是在Gen+1团簇的最稳态结构的基础上用Mn原子替代一个角位的Ge原子获得;纯锗团簇的稳态结构为空心的笼状或扁长的棒状构型,而GenMn(n=8-13)趋于以二十面体为基础生长,即掺杂Mn可以使锗团簇趋于密实结构生长;除Ge3Mn团簇的总自旋磁矩是5μB外,其他掺杂团簇总自旋磁矩都是3μB或1μB,而且主要是由Mn原子3d轨道电子提供的,且3d轨道的磁矩大小与4s,3d轨道间电子的转移程度有着直接的关系;计算得到的Mn原子居于中心的六棱柱形结构的Ge12Mn团簇,无论是几何结构还是化学活性方面都是最稳定的.

We report ab initio calculations of the structures, binding energy and total spin moments of GenMn （ n = 1 - 13 ） clusters using all electron density - functional method. Our results show that the small GenMn （ n = 1 - 7 ） clusters are formed by substituting one vertex site Ge - atom of the ground state Gen＋ 1 clusters with Mn at- om. For the larger clusters with n=8 - 13, the clusters are taking shape by encapsulating Mn into the empty Gen cages. The GenMn cluster grows in an icosahedral pattern but Gen cluster tends to be a hollow cage or a prolate configuration. When n≤7, the total magnetic moments of Ge, Mn clusters have a constant value （3 μB） expect the Ge3Mn （5 μB） cluster. When n=8-13, they are 1 μB expect Ge11Mn （3 μB） cluster. Furthermore, Mn atomic magnetic moment is mostly equal to the local magnetic moment of 3d state. It is the charge transfers among the 3d, 4s and 4p states of Mn atom that play an important role in the local magnetic moment of Mn and the total magnetic moments of GenMn clusters. For Ge12Mn cluster, the second -order difference of binding energy indicates it has higher stability than its neighbors and the HOMO -LUMO gap indicates the chemical inert- ness of the Ge12Mn cluster.